To gain an understanding of messenger RNA biogenesis using the vaccinia virus as a model system. To understand the genomic makeup of the virus and the regulation and expression of individual genetic elements and their functions in the replicative and infectious cycle of the virus. An analysis of the genetic elements of the virus using the technique of marker rescue to localize these elements to defined regions of the genome, thus gaining an insight into the controlling features of the genetic material vaccinia. To establish the vaccinia genome as a modified DNA genome for insertion of foreign genetic elements. This will allow a number of pertinent questions to be answered regarding gene regulation and expression as well as other potential uses of this novel eukaryotic cloning vector.